Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

5.12

1.25

2. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

3. For obtaining high COP, the pressure range of compressor should be

Low

High

Any value

Optimum

4. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant temperature

Takes place at constant pressure

Takes place at constant entropy

5. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Negative

Zero

Positive

6. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Evaporator and compressor

Condenser and receiver

Compressor and condenser

7. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

8. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.4

0.376

0.6

9. The boiling point of ammonia is

-30°C

-33.3°C

-10.5°C

-77.7°C

10. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

2 bar

15 bar

8 bar

Page 2 of 4

11. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Refrigerant cooling tubes

Capillary tubes

Condenser tubes

12. Which of the following is not a desirable property of a refrigerant?

Large latent heat

High risibility with oil

Good electrical conductor

Low boiling point

13. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Condenser

Condenser, absorber and separator (rectifier)

Evaporator

14. The freezing point of sulphur dioxide is

-75.2°C

-77.7°C

-135.8°C

-56.6°C

15. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Less

Same

16. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Ericson

Carnot

Stirling

17. Freon group of refrigerants are

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

Toxic

18. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

19. Critical temperature is the temperature above which

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

20. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Page 3 of 4

21. Rating of a domestic refrigerator is of the order of

5 tons

40 tons

10 tons

0.1 ton

22. A thermostatic expansion valve in a refrigeration system

None of the above

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

23. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

24. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Freon

Ammonia

Carbon dioxide

25. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 3

9: 1

1: 9

26. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Saturated liquid

Dry saturated vapour

Wet vapour

27. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

4.33

1.33

2.33

28. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

29. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Dry bulb temperature of air

Ambient air temperature

Dew point temperature of air

30. A bootstrap air cooling system has

Four heat exchangers

Two heat exchangers

One heat exchanger

Three heat exchangers

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31. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

32. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Always more than unity

Equal to unity

Always less than unity

33. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Normal cooling

Super-cooling

None of these

34. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

35. The domestic refrigerator uses following type of compressor

Centrifugal

Miniature sealed unit

Piston type reciprocating

Axial

36. The capillary tube, as an expansion device, is used in

Room air conditioners

Domestic refrigerators

Water coolers

All of these

37. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Rankine

Reversed Carnot

Rankine

38. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

39. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

40. Most thermostatic expansion valves are set for a superheat of

20°C

15°C

5°C

10°C

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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